Title: Nuclear Science for the Manhattan Project and Comparison to Today’s ENDF Data

Abstract

Nuclear physics advances in the United States and Britain from 1939 to 1945 are described. The Manhattan Project’s work led to an explosion in our knowledge of nuclear science. A conference in April 1943 at Los Alamos provided a simple formula used to compute critical masses and laid out the research program needed to determine the key nuclear constants. In short order, four university accelerators were disassembled and reassembled at Los Alamos, and methods were established to make measurements on extremely small samples owing to the initial lack of availability of enriched 235U and plutonium. I trace the program that measured fission cross sections, fission-emitted neutron multiplicities and their energy spectra, and transport cross sections, comparing the measurements with our best understanding today as embodied in the Evaluated Nuclear Data File ENDF/B-VIII.0. The large nuclear data uncertainties at the beginning of the project, which often exceeded 25% to 50%, were reduced by 1945 often to less than 5% to 10%. Uranium-235 and plutonium-239 fission cross-section assessments in the fast mega-electron-volt range were reduced following more accurate measurements, and the neutron multiplicity $$\overline{v}$$ increased. By a lucky coincidence of canceling errors, the initial critical mass estimates were close to the final estimated masses. Some images from historical documents from our Los Alamos archives are shown. Many of the original measurements from these early years have not previously been widely available. Through this work, these data have now been archived in the international experimental nuclear reaction data library (EXFOR) in a collaboration with the International Atomic Energy Agency and Brookhaven National Laboratory.

Authors:

Chadwick, Mark B. ^[1]

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+ Show Author Affiliations

1. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Publication Date:

Tue Nov 16 00:00:00 EST 2021

Research Org.:

Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE

Contributing Org.:

Office of Scientific and Technical Information (OSTI)

OSTI Identifier:

1972173

Report Number(s):

LA-UR-20-30028
Journal ID: ISSN 0029-5450; TRN: US2313769

Grant/Contract Number:  

89233218CNA000001

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Technology

Additional Journal Information:

Journal Volume: 207; Journal Issue: sup1; Journal ID: ISSN 0029-5450

Publisher:

Taylor & Francis

Country of Publication:

United States

Language:

English

Subject:

73 NUCLEAR PHYSICS AND RADIATION PHYSICS; nuclear science; Manhattan Project; ENDF nuclear data